Masaki Yasuoka

Seeding effects on crystallization and microstructure of sol-gel derived PZT fibers

Dense and fine micro-structured lead zirconate titanate (PZT) fibers were successfully fabricated by sol-gel process from lead acetate dehydrate, zirconium normal butoxide, and titanium isopropoxide. An addition of perovskite seed particles (2 wt%) can lower the formation temperature of the perovskite phase and a single-phase perovskite PZT fiber can be obtained by heat-treating the precursor fiber at 500°C. Crystallization of perovskite phase was improved with the seed content. The diffraction peaks of (200) and (002) in the PZT fiber with 6 wt% seed was better split than in the PZT fiber without seed, which indicates that the tetragonality of PZT fiber was increased by adding seed particles. Seed particles also affected microstructure development of the PZT fibers.

Reaction process and densification process of mixed α'/β'-sialon ceramics

Abstract The sintering behavior of mixed α′ β′ - sialon ceramics, fabricated from α-Si 3 N 4 , AlN and Ln 2 O 3 (Y 2 O 3 , Er 2 O 3 and Yb 2 O 3 ), was examined by high-temperature dilatometry, and the densification process was discussed through the consideration of chemical reactions to form α′- and β′-sialon and kinetical analysis of shrinkage. The formation of α′-sialon and melilite caused temporary retardation of the densification rate, while during the formation of β′-sialon the densification proceeded remarkably. The densification accompanied by precipitation of β′-sialon is ascribed to dissolution of residual α-Si 3 N 4 , α′-sialon with low solid solubility and melilite into a liquid, which may result in an increase of liquid volume and in a decrease of liquid viscosity. These phenomena are considered to induce the solution-precipitation process, particle disintegration process and cooperative flow process of the particle-liquid mixture, yielding to rapid shrinkage. The densification at the initial and middle stages and the reactions from α′-sialon and α-Si 3 N 4 to β′-sialon accelerated in the order of Y 2 O 3 > Er 2 O 3 > Yb 2 O 3 addition, because the liquidus temperature and viscosity of liquid formed decreased in the order of Y 2 O 3 2 O 3 2 O 3 addition.

DIELECTRIC PROPERTIES OF PB(ZR, TI)O3-DISPERSED MGO NANOCOMPOSITE

Ceramic nanocomposites with perovskite-type ferroelectric dispersoids have been studied in order to introduce ferroelectricity and piezoelectricity into structural ceramics. First, MgO matrix/BaTiO3 dispersed ceramic nanocomposites were fabricated, but the piezoelectric coupling factor, kp, of the nanocomposites was reduced to less than 5%. In the present work, MgO matrix/Pb(Zr,Ti)O3 (PZT) dispersed ceramic nanocomposites were studied to realize ceramic nanocomposites with larger kp values than MgO/BaTiO3. MgO/PZT ceramic nanocomposites were successfully fabricated by a pressure-less sintering method. The MgO/PZT nanocomposites exhibited a D–E hysteresis loop, and the ferroelectricity of the PZT dispersoid was confirmed. The tetragonality of the PZT dispersoid was decreased in comparison to that of monolithic PZT ceramics, however, the tetragonal-cubic phase transformation temperature of the PZT dispersoid was higher than that of the monolithic PZT. The decrease in the tetragonality was correlated to the incorporation of Mg ions into the PZT dispersoid. The MgO/PZT nanocomposites exhibited piezoelectricity after poling, and the kp value was about twice that of the MgO/BaTiO3 nanocomposites.

High Toughness Alumina/Aluminate: The Role Of Hetero-Interfaces

Silica doped alumina/aluminate materials present a combination of high strength and high toughness not achieved before in other alumina systems, except for transformation toughened alumina. We have associated the increase in toughness to crack bridging by anisotropically grown alumina grains with concurrent interfacial debonding of these grains. A HREM study of grain boundaries and hetero-interface structures in this material shows the absence of amorphous phases at grain boundaries. Local Auger electron analysis of fractured surfaces revealed the coexistence of Si and La at the grain facets exposed by the noticeable intergranular fracture mode of this material. It is concluded that a certain and important degree of boundaries weakness is related to both, presence of Si at the interfaces and existence of alumina/aluminate hetero-interfaces.

Microstructure control of silicon nitride by seeding rod-like β-Si3N4 particles

ABSTRACT Rod-like β-Si3N4 single crystal particles with a diameter of about 1μm and length of 5μm were grown from a mixture of β-Si3N4 and oxides, followed by acid rinse treatment to remove residual glassy phase. These β-Si3N4 particles were used as seed crystals to control microstructure of sintered silicon nitride under a low nitrogen gas pressure. The effect of seeding on the microstructure development and mechanical properties of silicon nitride were investigated.